I don't do the bar-ritos but I love the Buffalo Tofu bowl or salad. It's addicting, something about the hot sauce and celery/blue cheese combo, ha it's a proven flavor combo.
It's hard to compare to Pret as they are serving very different items. Both fast/casual, but Protein Bar has wraps, salads and bowls which heavily rely on quinoa as the source of protein. So if you don't like quinoa, you might not like it here. Pret has a more standard approach, but very nice quality of ingredients. I also love that they do the 1/2 sammy or wrap, it's a great pick with a small soup.
At Protein Bar, there are hits and misses, but if you do find something you like, it's a healthy alternative (though I agree, just b/c it says Protein Bar in the name, doesn't mean low in carbs). Plus, I like that it was founded by a Chicagoan, so it's a truly local chain. I love that Pret came to the US, and their ethics of donating any unused food. So they both have upsides and downsides, give it a try and see if you find something you like. I also like that you can buy the GT's Kombucha @ Protein Bar, hard to find in the Loop.
I don't go for the juices/smoothies or breakfast since I usually eat breakfast at home.
Cheers!